The first step in thyroid hormone formation is iodide transport in the thyroid, and is the concern of this project. The project includes studies 1) characterizing iodide transport mechanisms using anion transport inhibitors, 2) transfecting cells with anion transport proteins, and 3) expression cloning of iodide transport activity using cultured thyroid cells that respond to TSH but do not transport iodide. Initial studies focus on the use of specific probes for iodide transport; these probes include stilbene derivatives that interact with anion exchange proteins, and N-substituted anthranilic acid derivatives reported to block non-selective chloride channels in a variety of epithelial cell types. Effects of these compounds on sodium iodide uptake in thyroid cells suggest they may be useful in identifying and isolating iodide-transport proteins. Studies on cells transfected with a cDNA of an non-erythroid cell anion exchanger continue to support prior work that implicates this protein in iodide loss into the thyroid follicle, the site of thyroid hormone formation. Collaborative studies demonstrated the role of thyrotropin in sialylation of thyroglobulin in cultured rat thyroid cells. These observations have been extended to studies on thyroid tissue from patients with Graves' disease, where thyroglobulin is found to be hypersialylated. This contrasts with thyroglobulin isolated from endemic goiters which is both hypo-iodinated and hypo-glycosylated. The findings continue to support a role for sialylation in thyroglobulin secretion and iodination that is necessary for thyroid hormone formation.